This invention relates generally to pulse detonation engines and more particularly to rotary valves for controlling the flow of fuel and air in pulse detonation engines.
Most internal combustion engines currently used for propulsion rely on deflagration combustion whereby the combustion effects occur at relatively slow rates (i.e., less than the speed of sound within the combustible mixture) and at constant pressure. Detonation combustion, however, occurs at rates well in excess of the speed of sound and simultaneously provides a significant pressure rise. Because of the advantageous thermodynamic cycle, there is a high degree of interest in developing propulsive devices that rely on detonation combustion rather than deflagration combustion.
One such device is a pulse detonation engine that uses an intermittent combustion process to create a temperature and pressure rise by detonating a flammable mixture. The conditions for detonation are governed by the environment of the mixture (pressure, temperature, equivalence ratio, etc.) such that when enough energy is released to start ignition, the chemical kinetics occur at supersonic speeds. A pulse detonation engine is typically a tube of a specified length that is open at the aft end and includes some sort of valve device at the front end to keep the detonation process from traveling forward. In operation, a charge of air and fuel is fed into the tube through the valve, and the valve is then closed. Detonation of the fuel-air mixture is initiated by an igniter located in the tube, and the resulting detonation shock waves travel down the tube, raising both the temperature and the pressure of the products. The combustion products are expelled out of the open aft end, creating a pulse of forward thrust. When the shock waves have reflected within the tube to the appropriate conditions, a new charge is fed into the tube through the valve and the cycle repeats. It is generally desirable to generate pulses at a high frequency to produce smooth, nearly steady state propulsion.
The valve is provided at the forward end of the tube to prevent pressure waves from escaping out the front of the device and, more importantly, to prohibit the detonation flame front from traveling into the fuelair inlet system. The valve also must permit high inlet flows into the pulse detonation tube while maintaining a consistently good seal. The pulse detonation cycle requires that the valve operate at extremely high temperatures and pressures and must also operate at exceedingly high frequencies to produce smooth propulsion. These extreme conditions significantly reduce the high cycle fatigue (HCF) reliability of conventional valve systems, such as poppet or flapper-type valves.
Because of their oscillatory, xe2x80x9cback-and-forthxe2x80x9d nature, enabling such conventional valve systems to function reliably in a pulse detonation environment is a huge technical challenge, particularly given the inherent high inertia of these systems. One way to circumvent the HCF and inertia problems is to use a rotary valve instead of a poppet-type valve. Such valves typically employ a continuously rotating, ported plate. As the plate rotates, its ports periodically align either with a stationary plate with identical ports or with ports along the sides of the stationary pulse detonation chamber walls, thereby allowing intermittent flow into the pulse detonation chamber. Although a continuously rotating device will not encounter the same HCF reliability issues as an oscillating system, the currently available rotary valves could experience problems when used in the pulse detonation environment. For instance, the large pressures generated by the detonations can cause flexure of the rotating plate leading to binding of the plate and seal degradation. Also, maintaining a seal around the relatively large, flat surfaces of the rotating plate to isolate inlet flow and detonated products can be challenging. Another drawback of current rotary valves is that they often require the drive system for the rotating plate to be located in the primary gas path, resulting in flow reduction and performance losses.
Accordingly, it would be desirable to have a rotary valve for pulse detonation engines that overcomes the problems experienced by current rotary valves.
The above-mentioned need is met by the present invention, which provides a rotary valve for pulse detonation engines that includes a rotor rotatively mounted in the forward end of the pulse detonation tube and a plurality of transfer plenums for receiving fuel and air arranged around the rotor and partially disposed over the forward end of the tube. The rotor has a plurality of internal flow passages formed therein which periodically align with a plurality of inlet ports formed near the forward end of the tube as the rotor rotates. Each one of the transfer plenums is aligned with a corresponding one of the inlet ports so that the flow passages will establish fluid communication between the tube and the transfer plenums when aligned with the inlet ports.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.